The hydraulic adjusting cylinders are used to generate the rolling force in the rolling mill. For the rolling mill a high product selectivity requires that the rolling mill be capable of having large rolling force differences between the individual products which are to be produced by a given rolling mill stand.
It is known to apply the different rolling forces with two adjusting cylinders for each rolling mill stand. In this case, however, the production of a lower rolling force may involve the same friction losses as a higher rolling force which can give rise to difficulties in control. A greater part of the higher friction losses may contribute to loading of the seals, the piston rod and the piston in a piston-and-cylinder unit.
To adjust the rolling force in a rolling mill stand, especially in a strip rolling mill stand for hot or cold rolling, it is known (DE 40 10 662 C2), in maintaining in a simple way the percentage of rolling force fluctuations in the course of rolling force control over an entire rolling force range, so as to be exceptionally small, to provide both adjusting cylinders with a respective cylinder housing and a cylinder pin, with a hat-shaped piston which is guided in a cylinder collar and in which the central piston surface formed by the internal hat button and the annular piston surface formed by the peripheral rim of the hat shaped piston are subjected to the pressure medium independently from one another or individually, or in common. This system, however, provides a plurality of friction surfaces which can complicate the control of the system.